1. Field of the Invention
This invention relates to a molten metal flow rate (amount) control member for use in a molten metal discharging device which is mounted at a lower portion of a container such as a ladle or a tundish for molten metal such as molten steel, etc. and particularly to a slide gate plate for the flow rate control member.
2. Description of Related Art
A molten-metal flow rate (amount) control device for adjusting or ceasing discharge of molten metal such as molten steel, etc. in a molten metal container has been frequently used for a molten metal discharging device which is mounted at the lower side of a molten metal container. This type of molten metal flow-rate control device has a slide plate and a stationary (fixed) plate each of which is built in the device and has a nozzle hole therein, and the flow rate (amount) of molten metal is controlled by slidingly displacing the slide plate relatively to the stationary plate so the nozzles of the slide plate and the stationary plate are faced to each other to open a passage bore for molten metal through which molten metal is passed or the nozzles are not faced to each other (i.e., positionally deviated from each other)to close the passage bore for molten metal. An assembly (combination) of the slide plate and the stationary plate has been well known as a slide gate plate which constitutes an important part of the flow-rate control device for molten metal.
As described above, a conventional slide gate plate is mainly fabricated with a slide plate and a stationary plate, and a two-plate type or a three-plate type is usually used for the slide gate plate. A two-plate type slide gate plate is fabricated by assembling (combining) a single stationary plate 1 and a single slide plate 2 as shown in FIG. 1. In this case, two plates having the same thickness are used for the stationary plate 1 and the slide plate 2 respectively. On the other hand, a three-plate type slide gate plate is fabricated by assembling two stationary plates 3 and 4 and a single slide plate 5 so that the slide plate 5 is sandwiched between the upper and lower stationary plates 3 and 4 as shown in FIG. 2. Plates having the same thickness are used for the stationary plates 3 and 4. This three-plate type slide gate plate is disclosed in Japanese Laid-open Utility Model Application No. Sho-50-101514.
In the case where such a slide gate plate is worn or damaged during its use, with respect to the two-plate type slide gate plate, all plates constituting the damaged slide gate plate must be exchanged for new ones. On the other hand, with respect to the three-plate type slide gate plate, if a slide plate interposed between stationary plates is worn or damaged, only the slide plate is exchanged for a new one, however, if a stationary plate is worn or damaged, all the plates are disused and exchanged for new ones.
The following is the reasons why a plate whose surface is worn is exchanged for a new plate to reuse a damaged slide gate plate. If a worn plate (a stationary plate or sliding plate whose sliding face is worn) is polished for reuse, the polished plate itself would become thinner due to the polishing treatment, and thus proper sliding face pressure could not be obtained, so that molten metal may leak from a gap between the plates with high probability. Therefore, it has been generally avoided to repair a damaged (worn) plate with a polishing treatment or the like and reuse it.
However, the slide gate plate (each plate constituting the slide gate plate) itself is an expensive member, and it is liable to be greatly damaged due to its use under a severe environment, so that the exchange frequency of the slide gate plate (plates) increases. Therefore, the slide gate plate itself has been strongly required to be reused as much as possible in consideration of its cost. Particularly, it is uneconomical to disuse a plate and exchange it for a new one even when only the sliding face thereof is merely damaged.
In view of the foregoing, U.S. Patent application Ser. No. 150,585 filed on Jun. 7, 1971 (corresponding to Japanese Post-examined Utility Model Application No. Sho-57-36364) proposed a technique which could avoid the above problem. In this proposed technique, the slide plate and the stationary plate are transposed so that the right and left sides of the sliding reciprocating face thereof are positionally exchanged each other when the slide plate is worn due to its use for a prescribed period. With this transposition, each of the stationary plate and the slide plate comes into sliding contact with a new face.
However, with even the transposition technique as described above, it has been impossible to reproduce any plate whose sliding face is damaged during its use, and thus there has been achieved no excellent countermeasure which basically meets a requirement for reproduction of damaged slide gate plate (plates).
As described above, reusability of the slide gate plate (plates) has been required for a long time, and various polishing treatments to enable reuse of the plates have been considered and studied among skilled persons (experts) in the art. However, those persons have finally failed as follows: it has been impossible to obtain proper sliding face pressure, it has been impossible to remove only a damaged portion for a greatly-damaged plate by merely polishing the damaged plate slightly, so that reuse of the plate (slide gate plate) is impossible, etc. Accordingly, it has been practically adopted that damaged plates are not reused, and all plates are exchanged for new ones when they are used for a prescribed period or when they are damaged during its use.